Method of removing hydrogen sulfide from gases utilizing a polyvalent metal chelate solution and electrolytically regenerating the solution

Abstract

A process for the removal of H 2 S from sour gas streams is disclosed, the process being characterized by the use of a washing or contacting solution containing oxidizing polyvalent metal chelates of specified aminocarboxylic acids, the electrolytic regeneration of spent solution, and the co-production of hydrogen. Provision is also made for selective absorption of CO 2 .

What is claimed is: 
     
       1. A process for the removal of H 2  S from a sour gaseous stream comprising (a) contacting the sour gaseous stream in a contacting zone with an aqueous reaction solution at a temperature below the melting point of sulfur, the solution containing an effective amount of a reactant comprising an oxidizing polyvalent metal chelate of an acid having the formula ##STR3##  wherein from two to four of the groups Y are selected from acetic and propionic acid groups; from zero to two of the groups Y are selected from 2-hydroxy ethyl, 2-hydroxy propyl, and ##STR4##  wherein X is selected from acetic acid and propionic acid groups; and R is ethylene, propylene or isopropylene or alternatively cyclohexane or benzene where the two hydrogen atoms replaced by nitrogen atoms are in the 1,2 position; and mixtures thereof, and producing a sweet gas stream and an aqueous admixture containing crystalline sulfur, hydrogen ions, and the reduced polyvalent metal chelate of said acid, or mixtures thereof; said contacting zone comprising an anode section of an electrochemical cell, said cell also comprising a separate cathode section containing a cathode connected through an external electrical convention to the anode, the anode section and the cathode section being separated by a hydrogen ion permeable barrier,       (b) oxidizing the reduced polyvalent metal chelate or chelates of said acid in the aqueous reaction solution at the anode by supplying direct current to said cell, concomitantly allowing hydrogen ions to migrate to the cathode, and producing hydrogen at the cathode;   (c) removing sulfur from the aqueous reaction solution, and hydrogen from the cathode section.   
     
     
       2. A process for the removal of H 2  S from a sour gaseous stream comprising (a) contacting the sour gaseous stream in a contacting zone with an aqueous reaction solution at a temperature below the melting point of sulfur, the solution containing an effective amount of a reactant comprising an oxidizing polyvalent metal chelate of an acid having the formula ##STR5##  wherein from two to four of the groups Y are selected from acetic and propionic acid groups; from zero to two of the groups Y are selected from 2-hydroxy ethyl, 2-hydroxy propyl, and ##STR6##  wherein X is selected from acetic acid and propionic acid groups; and R is ethylene, propylene or isopropylene or alternatively cyclohexane or benzene where the two hydrogen atoms replaced by nitrogen atoms are in the 1,2 position; or mixtures thereof, and producing a sweet gas stream and an aqueous admixture containing crystalline sulfur, hydrogen ions, and the reduced polyvalent metal chelate of said acid, or mixtures thereof;       (b) regenerating aqueous admixture from step (b) electrolytically by passing admixture from step (b) through the anode section of an electrochemical cell and supplying direct current to said cell to oxidize reduced polyvalent metal chelate or chelates in the admixture at the anode and producing a regenerated aqueous admixture containing regenerated reactant, the anode section and the cathode section of said cell being separated by a hydrogen ion permeable barrier, concomitantly allowing hydrogen ions to migrate to the cathode section, and producing hydrogen at the cathode; therefor;   (c) removing regenerated aqueous admixture from said anode section, and molecular hydrogen from said cathode section; and   (d) returning regenerated aqueous admixture to the contacting zone.   
     
     
       3. The process of claim 2 wherein the oxidizing polyvalent metal chelate is the ferric chelate. 
     
     
       4. The process of claim 2 wherein the reactant comprises the ferric chelate of N-(2-hydroxyethyl)ethylenediamine triacetic acid. 
     
     
       5. The process of claim 2 wherein the aqueous reaction solution comprises a liquid absorbent selective for CO 2 . 
     
     
       6. The process of claim 3 wherein the aqueous reaction solution comprises a liquid absorbent selective for CO 2 . 
     
     
       7. The process of claim 4 wherein the aqueous reaction solution comprises a liquid absorbent selective for CO 2 .